The present invention is concerned with a method for the treatment of tumours and in particular, with a method for the treatment of tumours in the liver. The invention is also concerned with compositions suitable for such treatment.
Hepatoma (primary liver cancer) is one of the commonest causes of cancer death in the world with an estimated incidence of 1 million cases per year worldwide (Lencioni R and Bartolozzi C. The Cancer Journal, Vol 10, pp1-6). There is a considerable variation in its incidence with it being the most common in Asian countries. although it is now of increasing importance in the West. There are currently few effective treatment options available. Untreated, the average survival in this condition is of the order of 3 months. Liver resection may allow 5 year survival in approximately 40% of cases but very few patients are eligible for such treatment. Systemic chemotherapy has been of very limited value in the treatment of primary hepatic cancer, and attempts have consequently been made to deliver pharmacologically active agents directly to the liver using the technique of transarterial chemoembolisation (TAE). TAE combines the selective delivery of agents to hepatic tumours vascularized by the hepatic artery and thus their concentration in the tumour, with the concept of causing embolisation of the tumour and hence necrosis by ischemia. A wide range of chemotherapy agents have been delivered in this way, including doxorubicin, epirubicin and cisplatin (Choi, J. Cancer Control, Vol 3, pp407-413, 1996). Frequently, chemotherapeutic agents are emulsified with or dissolved in the contrast agent Lipiodol, which is an iodised poppy seed oil fatty acid ethylester. Uptake of iodised oil into tumours is thought to prolong contact of the chemotherapeutic agent with tumour, and the radioopaque nature of the medium enables progress of the infusion to be monitored by radiography.
Vitamin D is an isoprenoid compound made up of activated 5-carbon units. The most abundant form of vitamin D is vitamin D3, or cholecalciferol. Vitamin D3 arises from biosynthesis of 7-dehydrocholesterol, an intermediate in cholesterol biosynthesis. Vitamin D3 is metabolised in the liver to 25-hydroxycholocalciferol [25(OH)D3] which is a major form of Vitamin D circulating in the blood compartment. 25(OH)D3 is converted by the kidney to produce two principal dihydroxylated metabolites, namely, 1.25-dihydroxycholecalciferol [1.25(OH)2D3] and 24,25-dihydroxycholocalciferol [24R,25(OH)2D3].
1.25(OH)2D3 is the most biologically active naturally occurring form of vitamin D3 and is transported in the bloodstream to its major site of action in the mucosal cells of the intestine, where calcium absorption is stimulated. Thus vitamin D3 may be regarded as a prohormone because it is converted to a metabolite that acts analogously to a steroid hormone. It regulates calcium and phosphorous metabolism particularly in the synthesis of the inorganic matrix of bones.
Therapeutically, 1.25(OH)2D3 and certain other analogues of Vitamin D3 are used to counteract deleterious effects of dietary deficiency of Vitamin D (rickets), or in the treatment of diseases characterised by abnormalities in the synthesis of or response to Vitamin D such as hypophosphatemic vitamin D-resistant rickets and renal osteodystrophy (renal rickets). A further use in the calcification-related disease osteoporosis is distinct from assuring vitamin D nutritional adequacy. Here, the rationale is directly to suppress parathyroid function and reduce bone turnover (Goodman and Gilman, The Pharmacological basis of Therapeutics. Pub. 1992, The McGraw Hill Companies Inc). Finally, a recent use of Vitamin D3 analogues is in the treatment of the cutaneous disease psoriasis.
Experimental studies have shown that Vitamin D3 receptors are present on a range of cell types and so the understanding has arisen that the Vitamin D endocrine system is involved in the modulation of a number of fundamental cellular processes not directly related to calcium homeostasis (Pols, HAP et al, J Steroid Biochemistry, Vol 37, pp873-876, 1990). Included amongst the cells bearing Vitamin D3 receptors are a number of malignant tissues or cell lines derived from tumours. The presence of receptors on some cancer cells has been shown to have a functional significance in a number of cases, and the literature contains reports of Vitamin D3 and analogues being able to inhibit the proliferation of melanoma, osteosarcoma and breast carcinoma cells (Deluca HF and Ostrem V, Advances in Experimental Medicine and Biology, Vol 206, pp413-429, 1986) colon adenocarcinoma cells (Cross HS et al Journal of Nutrition, Vol 127 Suppl. pp2004-2008, 1995) and hepatic tumour cells (Tanaka Y et al, Biochem Pharmacol vol 38 pp449-453, 1989).
This effect in vitro has given rise to the hope that Vitamin D3 and analogues could be used in the treatment of cancers. Vitamin D3 compounds are listed among xe2x80x9cunconventional cancer therapiesxe2x80x9d (British Columbia Cancer Agency publication; 600 West 10th Ave, Vancouver, BC, Canada), and clinical trials have attempted to show an effect. Unfortunately, attempts to use naturally occurring analogues of Vitamin D3 such as 1.25(OH)2D3 have not been associated with the successful treatment of cancer and indeed have rarely been attempted. This is due in large part to the observation that for growth reduction of cancer cells to be caused by Vitamin D3, supraphysiological concentrations are needed (Pols et al-ibid). The consequence of this is that before anti-tumour properties of the treatment can be expressed, the effects of Vitamin D3 on calcium homeostasis are expressed to an excessive and dangerous degree, leading to life-threatening toxicity from hypercalcaemia.
In an attempt to overcome this problem, and to disassociate the hypercalcaemic effect of Vitamin D3 from its actions on cell differentiation, the pharmaceutical industry has expended much effort on the search for synthetic analogues that are devoid of an effect on calcium metabolism, and might therefore be useful for the treatment of cancer or other diseases. This approach has met with some limited success. For example, the analogue Calcipotriol has been synthesized which contains a 22-23 double bond, a 24(S)-hydroxy functional group, and carbons 25-27 incorporated into a cyclopropane ring. This compound has receptor affinity similar to that of 1.25(OH)2D3, but it is less than 1% as active as 1.25(OH)2D3 in regulating calcium metabolism. Calcipotriol has been studied extensively as a potential treatment for psoriasis (Goodman and Gilman, The Pharmacological Basis of Therapeutics Pub McGraw Hill, 1992). However, despite its reduced effect on calcium metabolism, calcitriol is used topically in order to avoid systemic hypercalcaemia. Examples have also been disclosed of synthetic Vitamin D analogues claimed to be useful for the treatment of tumours which have reduced effects on calcium metabolism (U.S. Pat. No. 4,891,364, Jan 2 1990). Also, attempts have been made to treat certain cancers locally. Thus, Bower M et al treated breast cancer topically with Calcipotriol (Lancet vol 337: No 8743 pp701-702). Of the 19 patients treated, only 3 showed a significant response and 1 a minimal response. Moreover, even though this synthetic analogue has a drastically reduced effect on calcium metabolism (vide supra) and even though the treatment was locally restricted to skin around breast cancer lesions, still 2 of the 19 patients became hypercalcaemic during treatment.
Thus, despite the interesting findings of basic researchers and the intensive efforts of the pharmaceutical industry, the application of Vitamin D compounds to cancer therapy has not been successful. The key limitation has been either an inherent lack of activity, or the low therapeutic index (ratio of effective dose to toxic dose) of Vitamin D3 which has made its use so difficult.
We have found that, surprisingly, regional delivery to the liver of a vitamin D compound, such as vitamin D3 or a precursor, metabolite or analogue thereof, avoids the production of hypercalcaemia, even at high doses of the vitamin D compound. For example, despite the fact that therapeutic oral and intravenous doses of 1.25(OH)2D3 are typically in the order of 0.5 to 3 mcg/day (at or beyond which level there is a distinct risk of hypercalcaemia developing), we have shown (Example 2) that doses of at least 10 mcg/day can be administered intraarterially to the liver without any observable systemic toxicity.
A reasonable conclusion of this observation is that the avoidance of hypercalcaemia after such high doses of Vitamin D compound is due to increased retention of the Vitamin D compound in the liver, or degradation in the liver (a first pass effect). However, neither of these occurrences could have been predicted for the following reasons: The dose provided is much higher than physiological levels, and thus, although arterial infusion would bring the Vitamin D compound into contact with cells bearing Vitamin D receptors, they would not be expected to be capable of trapping all the Vitamin D compound. Concerning degradation, the major metabolic activity of the liver is applied to compounds entering via the hepatic portal route, not the hepatic artery. Moreover, as was discussed above, the liver is one of the sites of activation of Vitamin D and would not necessarily be expected to remove Vitamin D compounds from the blood. The precise reasons why the Vitamin D compound induce less hypercalcaemia after hepatic arterial delivery are not known.
Regional delivery of Vitamin D3 to the liver has not only been shown to be safe, but in 4 of 7 patients had at least a limited response to treatment as indicated by changes in their rate of rise of tumour marker.
Thus, not only has the surprising ability to administer large doses of Vitamin D compound to the liver by regional delivery been demonstrated, but also indications of a beneficial effect on disease progress have been obtained.
Accordingly, the first aspect of the present invention consists in a method of treating a tumour in the liver of a subject including administering to the subject a pharmaceutically effective amount of at least one vitamin D compound selected from the group consisting of vitamin D, a precursor of vitamin D, or a metabolite or analogue thereof, wherein the vitamin D compound is regionally delivered to the liver.
The regional delivery of the vitamin D compound may be achieved by intraarterial delivery or delivery via the portal vein. Preferably the vitamin D compound is delivered intraarterially. Particularly preferred is where the vitamin D compound is delivered by intraarterial infusion via the hepatic artery.
The method of treatment of the invention may be used to treat primary or secondary cancers of the liver. The method of the invention is particularly suitable for the treatment of hepatoma (primary liver cancer) in a subject. The method of the invention may also be used to treat secondary cancers in the form of metastases in the liver, for example, metastases of colorectal cancer, lung cancer, breast cancer, prostate cancer, pancreatic cancer or renal cancer. The secondary cancer may be a sarcoma. The method of the invention may be used to treat primary or secondary liver cancers in the liver.
Preferably the vitamin D compound is vitamin D3 or a precursor or metabolite thereof, although the vitamin D compound may be an analogue of vitamin D3.
The vitamin D analogue compound may be selected from any suitable analogue, for example, 1.25(OH)2D3 (1-25-dihydroxycholecalciferol), OCT (22-Oxacalcitirol), MC903 (calcipotriol) or EB1089 (1 xcex1.25 (OH)2 22.24 diene 24.26.27 trihomo D3).
The metabolite of vitamin D may be a hydroxylated or other product of vitamin D or its analogues.
The effect of the vitamin D compound on tumours is very dose dependent and there is therefore advantage in delivering high concentrations of the vitamin D compound to the tumour. However, the limited solubility of vitamin D compounds in a conventional carrier such as aqueous media places an upper limit on the amount of compound that can be delivered to the tumour.
We have found that very high concentrations of a vitamin D compound, such as 1.25(OH)2D3, can be achieved by dissolving the compound in a pharmaceutically acceptable oil. For example, 2 mg of 1.25(OH)2D3 can be readily dissolved in 1 ml lipiodol. This high solubility allows for very high concentrations of vitamin D compound to the tumour. A further advantage of using an oil as the carrier for the vitamin D compound is that some oils are concentrated in certain tumours allowing the achievement of very high tumour concentrations of the vitamin D compound. Moreover, another advantage of achievement of high concentrations is that some vitamin D compounds that are inactive at low concentrations may become active at the much higher concentrations achieved when an oil is used to dissolve the compound.
Accordingly, in a second aspect the present invention consists in a method of treatment of the first aspect wherein the vitamin D is delivered as a solution of the vitamin D compound in a pharmaceutically acceptable oil.
The oil may be an iodised oil such as lipiodol although clearly the presence of iodine, while possibly being useful to allow infusion to be monitored radiographically, is not an essential feature of the oily agent. Furthermore, the oily agent needs only to (1) incorporate large amounts of Vitamin D compound and (2), if possible, be taken up into tumours being treated. Therefore, to one skilled in the art, the carrier could also be deemed to include other oils and chemically modified oils used in the pharmaceutical industry such as Cremophor (polyoxyethylated castor oil). Examples of oils for intra-arterial tumour treatment are disclosed in U.S. Pat. No. 4,578,391, which disclosure however is solely concerned with the dissolution of sparingly oil-soluble or water soluble anti-tumour drugs for infusion. Known formulations for intravenous use (Calcijex(copyright) calcitriol injection marketed by Abbot Laboratories, as described in the Physicians Desk Reference, ibid, and also formulations disclosed in U.S. Pat. No. 4,308,264) are aqueous solutions and their use in the treatment of cancers has not been reported. Moreover, their low calcitriol content would make them particularly unsuited to intra-arterial administration to the liver.
Further suitable carriers include multicomponent systems capable of incorporating lipophilic materials such as liposomes and microemulsions.
Tamoxifen, an oestrogen receptor antagonist, has been shown to significantly, but modestly, improve survival in human hepatoma. It has also been shown that tamoxifen increases vitamin D receptor expression on breast cancer lines. We believe that tamoxifen""s effect on hepatoma may be due to its effect on vitamin D receptor expression, making the tumour more sensitive to endogenous vitamin D. Tamoxifen and oestrogen or oestrogen-like compounds are therefore expected to significantly increase the effect of vitamin D therapies in cancers such as hepatoma and that this will significantly increase response whilst allowing lower doses of the vitamin D compound, thus avoiding hypercalcaemia and other complications.
Accordingly in a third aspect, the present invention consists in a method of treatment in accordance with the first and second aspects of the invention, the method further including administration of a compound capable of increasing vitamin D receptor expression is also administered.
The compound capable of increasing vitamin D receptor expression may be tamoxifen or other oestrogen or oestrogen-like compound.
The compound capable of increasing vitamin D receptor expression may be administered before, concurrently or after administration of the vitamin D compound.
In a fourth aspect the present invention consists in a composition suitable for the treatment of a tumour in the liver, the composition including a pharmaceutically effective amount of a vitamin D compound selected from the group consisting of vitamin D, a precursor of vitamin D, or a metabolite or analogue thereof dissolved in a pharmaceutically acceptable oil.
The pharmaceutically acceptable oil is an iodised oil such as iodised poppy seed oil. The pharmaceutically acceptable oil may be a non-iodised oil, for example, poppy seed oil.